Methods and apparatus for image display of sound waves and utilizations thereof

ABSTRACT

A device employing a piezo-optic cell having a thin layer of aligned liquid crystals which is illuminated by polarized light and viewed through a polarized analyzer to give a real-time visual image in color of the acoustic wave pattern incident thereon. The acoustic wave pattern is typically an acoustic image of an insonified object such that the resulting device is useful in non-destructive testing for industry and medicine. The acoustic wave pattern can also be the human voice (helpful in teaching speech to the deaf) and music (for pleasurable and informative visualization of the musical sound). By use of a reference acoustic wave this device may be utilized to obtain a holographic image.

Elite ttes atent [1 1 Greguss 1451 Aug. 27, 1974 METHODS AND APP s- TUS FOR GE DISPLAY OF SO WAVES AND UTILIZATIONS THEREOF [75] Inventor: Pal Greguss, Long Island, NY.

[73] Assignee: Vari-Light Corporation, Cincinnati,

Ohio

[22] Filed: Mar. 23, 1972 [21] Appl. No.: 237,404

Primary Examiner-James J. Gill Attorney, Agent, or F irm-Curtis, Morris & Safford; A. Thomas, S. Safford A device employing a piezo-optic cell having a thin layer of aligned liquid crystals which is illuminated by polarized light and viewed through a polarized analyzer to give a real-time visual image in color of the acoustic wave pattern incident thereon. The acoustic wave pattern is typically an acoustic image of an insonified object such that the resulting device is useful in non-destructive testing for industry and medicine. The acoustic wave pattern can also be the human [56] References Cited voice (helpful in teaching speech to the deaf) and UNITED STATES PATENTS music (for pleasurable and informative visualization of 3,597,043 8/1971 Dreyer 350/149 the musical sound). By use of a reference acoustic ,5 8/1971 Cohen eta! R wave this device may be utilized to obtain a holo- 3,700,805 10/1972 Hanlon 178/73 D graphic image 3.707.323 12/1972 Kessler et a1. 350/161 FOREIGN PATENTS OR APPLICATIONS 19 Claims 6 Drawing Figures 1,194,544 6/1970 Great Britain 73/675 H ll l PATENTEU AUS 2 71974 FIG. i

METHODS AND APPARATUS FOR IMAGE DISPLAY OF SOUND WAVES AND UTILIZATIONS THEREOF The present invention relates to the general field of mechanical-to-optical wave form conversion which finds particular application in the insonification of objects with conversion of the resulting acoustic image to a visual display. Such use with ultrasonography and the like has considerable potential for many uses including non-destructive testing and diagnostics. In the following discussion, it should be recognized that much of the exemplification of this invention will be in terms of acoustical waves including ultrasonics through infrasonics, but in its broader aspects is applicable to mechanical waves of all frequencies, in general.

It has long been recognized that acoustical waves could be utilized in many ways similar to x-rays and in applications where x-ray utilization is impossible or prohibitive, if only an acceptable technique for recording and/or comprehending the acoustical wave patterns could be developed. The most desirable method of comprehension would be a real-time display of the insonified object which when recorded in holographic form, would yield a three-dimensional reconstruction.

It is accordingly an object of the present invention to provide a method and apparatus for achieving such a display.

The development of an acoustical-to-optical converter which gives a picture-like information of the acoustic field pattern has met with varying degrees of success during its development over the past half century. In more recent years these efforts have also concentrated on obtaining acoustic holograms, the first of which was made by the applicant on silver-haloid-based sonosensitive plates in 1965. Some of the main drawbacks of these sonosensitive plates were that they required relatively high ultrasonic intensity and long exposure times and naturally could not give a real-time image.

In another prior art method, the acoustic signal emerging from the insonified specimen could be detected by a scanning acoustic receiver. The latter is in the form of a transducer which converts the acoustic signal into an electrical signal. By the use of an electronic reference system and a modulated light source synchronized with the receiver, a holographic transparency is then recorded and reduced for optical reconstruction of the acoustic image. In addition to being complex and expensive, this technique still has many of the drawbacks of the applicants aforementioned earlier developments. Although it achieved a greater sensitivity, its lack of a real-time image makes it completely unsuitable for biological-medical applications and the like.

Real-time ultrasonic holography was reported to have been achieved about six years ago in a technique which has recently been described on pages 30 and 31 of Product Engineering for January 1972 in an article entitled Acoustical Holograms Seek Out Flaws and Voids in Materials". It has been recognized since 1929 that a liquid surface will deform due to sound pressure. This concept has been used to form a visual image of the acoustic field on the surface of a body of water in which the object being insonified is immersed. Among the drawbacks of this technique are that the liquid surduced.

Over 20 years ago, it was proposed to use thermally induced color changes of certain crystals coated on a suitable absorbing material in response to the acoustic image projected onto the absorbing material to give a visual color image with the colors indicating the sound intensities of the acoustic image in reaction to the temperature variation in the absorber. Temperaturesensitive liquid crystals have been utilized with some degree of success, although the time and intensity required to obtain the necessary color change and the insufficient resolution have made this unsuitable for practical purposes.

Another report (on pages 158 of Materials Evaluation for August l968 in an article entitled Use of Color Display Techniques to Enhance Sensitivity of the Ultrasound Camera) noted that prior electronic scanning devices (of the type previously discussed) displayed the resultant image in varying shades of gray (where the human observer can distinguish no more than 5 10 different degrees of shade) and therefore the sensitivity of the camera is quite low. This article describes a device for displaying the differential acoustic impedance changes by a color TV display thereby resulting in increasing the sensitivity which can be de termined by the eye of the observer by several orders of magnitude.

It is accordingly a further object of the present invention to provide an acoustical-to-optical converter which displays a real-time visual image of the sound field in color, with great simplicity, good sensitivity and resolution, and relatively low acoustic intensity requirements.

According to a preferred embodiment of the present invention, these advantages can be obtained by the utilization of a piezo-optic cell of the type described in US. Pat. No. 3,597,043, issued Aug. 3, 1971 (the description of which is incorporated herein by reference) with a sufficiently thin liquid crystal layer, effectively coupled to the source of an acoustic wave pattern emanating from the object to be observed, illuminated by polarized light passing through the cell and viewed through a relatively rotatable polarizer (or a functional equivalent). Note for example, if a dichroic liquid crystal compound is used, the liquid crystal may serve as the first polarizer and only one additional polarizing filter is needed, as an analyzer. The optical element of the aforementioned patent is a piezo-optic cell which functions as a recording media for converting mechanical waves into corresponding visible colored patterns. Although the patentee recognized the response of his cell to acoustic energy, there is no teaching nor recognition that such a cell would be useful in obtaining a good quality visual image of an insonified object. However, applicant in connection with his decades of work on developing acoustical-to-optical converters, recognized the possibility of adapting the patentees cell to function as an effective acoustical-to-optical converter having sufficient sensitivity and resolution to give the desired visual image of the insonified object. This cell used for this purpose is currently referred to in the art as AOCC (Acousticalto-Optical Converter Cell).

After having conceived and constructed various devices embodying his invention, applicant recently became aware of another report published in Applied Physics Letters, Volume 18, No. 4, Feb. 15, I971 at pages 105 107, entitled Effect of Ultrasound on A Nematic Liquid Crystal", which in its very last paragraph suggested that there may be a possibility of using a cell having aligned nematic liquid crystals as an image detector with sufficient sensitivity provided the cell is biased with an electric field. In contrast, applicant has proven that no electric biasing is required. In fact, such biasing may mis-orient the liquid crystals. Additionally, contrary to the implications of this latter article (which used 60 80x magnifications) it develops that when used as an acoustic hologram recording device, in spite of the fact that the wave length of light is approximately 500 times smaller than that of sound, the visually reconstructed picture of the insonified object will be about the same size as the original object. In acoustic holography this vast difference in the recording acoustic and reconstructing light wave lengths is usually a significant problem. The present invention in utilizing the piezo-optic cell surprisingly appears to function not only as an acoustical-to-optical image converter, but also as a wave length transformer, a unique property making it very valuable in holography.

Without wishing to be bound thereby, the applicant suggests the following theory. In the piezo-optic cell the nematic liquid crystal molecules are sandwiched in a thin layer between two glass plates. The aforementioned patent indicates that when its lubricant is used on "the surface of one of the plates in contact with the liquid crystal film such substance will remove any effect of surface orientation of the supporting plates. With the attractive forces of the plates effectively reduced (whether by said lubricant or functionally equivalent means), the liquid crystals in said film may be characterized as being substantially in their free state. The birefrigence is uniform across the field. When an acoustic wavefront is acting on this sandwich assembly, the mechanical action of the acoustic wave shifts the molecules of the liquid crystals out of their original alignment. These disorientations may function as a diffraction grating, the interaction of the line spacings of which functions to help re-create the acoustic image in a correspondingly sized visual image causing the piezooptic cell to function as a wave-length converter.

One consequence of this is that linearly polarized light passing through the liquid crystal layer at any given point is rotated through an angle which is related to the intensity of the acting acoustic beam. This rotation can be visualized by looking at the sandwich assembly through a suitably oriented analyzer. The intensity distribution of the acoustic field will appear in a corresponding distribution of varying colors.

Even if the piezo-optical cell is considered only as an acoustic image display; this is quite sensitive, since in full color very slight absorption differences in an insonified object can be detected. Naturally, this display represents a new visual experience to the observer, since it has no natural color associated with the previous experiences of the observer. But this may be useful in enhancing the observers ability to detect and interpret details in the visualized intensity distribution of the acoustic field. This could for example be used in biomedical research and could lead to the discrimination between non-neoplastic, sterile, inflammatory lesions and malignant tumors, etc.

As an acoustic hologram recording media, the piezooptical cell can be considered to act partly as a volume hologram and so as a hologram which can be recon structed with white light. That this is the case is illustrated by the floating E experiment discussed below.

Using the piezo-optic cell a display for acoustic ho lography, i.e., to visualize the interference fringe issuing from the interaction of the object and reference acoustic wavefronts, we have the advantage of not being restricted by the aperture of the recording media. It is, however, well known that the resolution of an optical image (both transverse and depth) is dependent on the size of the aperture of the imaging system. Thus, if image accuracy is an important factor, the aperture of the optical system (in this case the physical size of the hologram) must be large enough to resolve the detail in the image at least to the degree of the desired accuracy. This problem is even more fundamental in acoustic than in optical holography due to the differences in the recording and reconstructing wave lengths.

The acoustic hologram can be created in the usual manner by using two separate acoustic transducers, one supplying the reference wavefront and the other insonifying the object to supply the object wavefront. The same effect can be achieved by splitting the beam from one acoustic transducer into two separate reference and object beams. A single acoustic transducer can also be used by having its beam incident on the piezo-optic cell at a sufficiently acute angle to have a traveling wave established in the cell. Experiments indicate that a practical limit at present on the viewing angle is fi0 (this is not to be confused with the angle of incidence of the ultrasonic beam on the cell, just mentioned).

The frequency range for this invention is the whole acoustic spectrum. By varying .the frequency, one changes the color patterns of the image created at a given polarizer setting. It may thereby be possible to emphasize different features of the image by more effective color contrasting (or alternatively merely by adjusting the polarizer setting). Similar results can be achieved by use of multiple selected frequencies. Thus, by matching the frequencies (or the wave length) with the structure of the object being analyzed (e.g., soft tissue or foundry castings) one can often obtain more effective and detailed information. Image size can also apparently be somewhat controlled by altering various factors including the coupling media, shape of the cell, etc.

In addition to the broad inventive concept disclosed above and the specific applications thereof to be discussed below in conjunction with the drawings, this invention may have the following more specific utilizations. For example, the visualized acoustic image developed in the transparent piezo-optic cell may simultaneously have projected thereon a super-imposed optical image. It might even be possible to have the two optic and sonic-derived visual images related as to size and content so that one would view in essence a double exposure indicating the exterior and outline of the object being viewed and at the same time an x-ray like visualization of the internal structure of the object.

As previously suggested herein, this invention could find particular application in the medical examination of soft tissue, tumors and the like. The differentiation of tumors from surrounding soft materials is particularly useful since sound waves react to such materials in a manner different from x-rays and therefore can often differentiate to a better degree. The invention can also be used as well in diagnostics as in nondestructive testing, in analyzing reflections within such structures or transsonification of these structures and the tissue therebeyond.

Because of the penetrating ability of acoustic waves in water, this invention can find application as an underwater radar display useful for submarines, in oceanography, and in night-time or deep-skin-diving.

Similarly, this invention could be utilized as a visual aid for deaf persons. A significant problem with persons who have never had audible sound experiences during their lifetime, is that they have great difficulty learning to speak because they can never monitor their own voices to learn whether they are making the correct sounds for creating speech. With this invention it would be possible to identify and teach visual display patterns of the various sounds. These patterns could probably be learned within a year or so in much the same way that a written foreign language is learned. One problem is that the wave lengths of audible sound are too large to be displayed on a piezo-optic cell of convenient dimensions so that such a cell is not suitable for direct visualization of the characteristic sound patterns. If, however, an ultrasonic frequency is modulated with the audible sound to be visualized, the display could be formed thereby of a convenient size. This can be achieved for example by using a ceramic transducer with a fundamental frequency identical to the carrier frequency of an FM radio and driving it with an FM signal. The field pattern of this ceramic transducer visualized by the piezo-optic cell would yield a recognizable pattern of the audible sound. Since this pattern would be in color, it would be easier to memorize and therefore to learn how to hear by seeing. An additional feature could be to use two ceramic transducers at right angle in a stereophonic manner and obtain recognizable interference patterns.

The utility of this invention can be further expanded by utilizing optical and/or sonic lenses and even fiber optics. These can be used to focus or otherwise alter the sonic image prior to conversion or to better visualize the optical image created after conversion.

Concerning the piezo-optical cell itself, the thickness of the entering glass panelshould preferably follow the following equation: H (thickness of glass) =n(L/2) where n is an odd integer and L is the wavelength in glass.

One can use multiple piezo-optic cells. This can occur as a side by side mosaic in an attempt to achieve a large display. The need for such a mosaic is in order to maintain the required spacing between the glass plates without having the weight and thickness of the glass become prohibitively large in order to have the strength to do so. An alternative might be to have a large single cell with a grid of spacers which would thereby serve the multiple use of an array of reference points. The piezo-optic cells could also have multiple liquid crystal layers in depth by having one or more very thin glass sheets (or the like) interleaved between said layers. This would give a greater display depth and yet not adversely affect the normal alignment of the liquid crystals by having the spacing forming each individual liquid crystal layer being too large.

In a typical piezo-optic cell according to my invention there is a thin layer of nematic liquid crystal between two glass plates, the inner surfaces of which plates have been coated with a thin layer (probably monomolecular) of lecithin or compounds with similar effect. This layer thickness of liquid crystals follows typically the following equation FH /C K (a constant) which F is frequency and which K depends upon the liquid crystal material used. H is the thickness of the liquid crystal layers and C is the sound velocity in the liquid crystal layer said layer is typically about 0.001 inches thick. The glass facing the sonic generator is about 1/16 of an inch thick. The opposite sheet of glass is about one-quarter of an inch thick. The sandwich of glass and liquid crystals are preferably sealed and positioned along the edges by an epoxy cement. The overall size of these cells has been approximately two to ten inches, but in actual fact is limited at the lower end merely by aperture considerations and at the upper end by the physical problems of maintaining the inter-glass spacing sufficient to retain the required alignment of the liquid crystals therein. If the sizes get too large there is a gravitational tendency of the glass to sag in the horizontal position or of the weight of the liquid crystal solution to bulge the glass, if the cell is held in the vertical position.

Currently as a practical matter the liquid crystal thicker layer is no more than 0.010 inches thick, because a layer tends to become translucent.

As it will be discussed below, this invention can utilize a piezo-optic cell of the type described in FIG. 3 of the aforementioned patent where one of the sides of the cell has a reflecting surface. It is possible that the glass plate on the reflecting surface side could be replaced by a polished metal provided the alignment of the liquid crystals is not thereby adversely affected.

It has been suggested by applicant that the ultrasonic energy be pulsed and the visual image thereof be viewed with strobescopic light to thereby obtain a holographic cross-sectional image of the solid object being trans-sonified at a given depth thereof.

It has also been suggested by applicant that the sound beam be scanned to give an electrical image that can be transmitted by radio and, can be reconstructed by a sonic transducer to give a sonic beam incident on a pieZo-optic cell at a remote location to give a very thin holographic television display.

In this specification and the accompanying drawings 1 have shown and described preferred embodiments of my invention and have suggested various alternatives and modifications thereof; but it is to be understood that these are not intended to be exhaustive and that many other changes and modifications can be made within the scope of the invention. These suggestions herein are selected and included for purposes of illustration in order that others skilled in the art will more fully understand the invention and the principles thereof and will thus be enabled to modify it and embody it in a variety of forms, each as may be best suited to the conditions of a particular use.

IN THE DRAWINGS:

FIG. 1 is a schematic plan view of a device embodying the present invention.

FIG. 2 is a schematic sectional view of a piezo-optic cell.

FIG. 3 is a schematic plan view (partially exploded for clarity) of an alternative embodiment of the present invention illustrating a solid instead of a liquid coupling.

FIG. 4 is a schematic plan view (partially exploded for clarity) of a third embodiment of the present invention illustrating the use of a reflecting piezo-optic cell.

FIG. 5 is a schematic plan view of a fourth embodiment of the present invention illustrating that the direct line up of the ultrasonic generator, the object to be viewed, and the piezo-optic cell is not required, but can be achieved by reflection.

FIG. 6 is a schematic side elevational view of a fifth embodiment of the present invention illustrating the creation of an image from an ultrasonic generator coupled by solid contact between the object and the edge of the piezo-optic plate.

In the embodiment illustrated in FIG. 1, a box 10 conveniently constructed of a clear acrylic plastic is filled with water 12 which has immersed therein at one end of the box 10 a piezo-optic cell 14 and opposite therefrom an ultrasonic generator 16. The water 12 preferably has a small amount of wetting agent such as l/lO percent Aerosal OT to give good coupling between the generator 16 and the cell 14 so as to carry the sonic waves therebetween with little loss. The ultrasonic generator 16 is a l to 3 MHz piezo-electric transducer. The generator 16 is directed at the object 18 which is to be transsonifled and therebeyond at the cell 14. The object 18 is here illustrated as a metal cube having a hole 20 drilled therein. At the end of the box 10 adjacent to generator 16 is a linear polarizer 22, a difuser 24, and a light source 26 for creating polarized light incident on the back of the piezo-optic cell 14. The visually converted ultrasonic image of the object 18 and its hole 20 appears on the flat surface of the cell 14 when viewed through a polarizing filter 28. It will be appreciated that the relative positioning of these various elements can vary to a large degree and still give the desired effect within the scope of the present invention. For example, the cell 14 could form the front of the box 12 and be integrally constructed therewith and the front plate 30 of the cell 14 could have a polarizing surface (provided that the polarized light incident thereon is rotated at a desirable angle or is rotatable with respect thereto so as to achieve any desired angle). As discussed in the aforementioned patent, these two polarizers 22 and 28 need not be crossed.

The piezo-optic cell 14 has a thin plate of glass 32 which should function as an acoustic window. Therefore, as previously indicated, it would preferably have a thickness governed by the previously discussed equation. The liquid crystal layer 34 is apparently aligned by the effect of the lecithin layers 36 and 38 on either side thereof. The function of this lecithin, or its equivalent, is discussed in the aforementioned patent as being a lubricant, but more properly is probably a positive orienting means in that one end of the lecithin molecule is attracted to the polarity of the glass and the other end of the lecithin molecule is attracted to the liquid crystal layer, thereby counteracting the effect of surface orientation of the glass. The plates 30 and 32 are fixedin spaced relation by epoxy cement 40.

The water 12 preferably is degassed and may have additives to enhance its coupling function. Alternative liquid couplers such as glycerine can also be used. The box 10 can be constructed as an anechoic liquid chamber for the coupler 12 to eliminate any ultrasonic reflections impinging upon the piezo-optic cell 14 and thereby give a clearer image thereon. Impedance matching layers may be put on the glass surface to reduce the reflections of the glass surface to the piezooptic cell.

It is possible that air could be used as a coupler 12 but would be very poor, not only because of the transmission losses, but also because of the large size of the cell 14 which would be required to view an image of a relevantly small object 18.

A good alternative coupler is'the solid object 18 itself in direct contact with the generator 16 and the cell 14, as in FIGS. 3 and 4. In FIG. 3 the ultrasonic generator 16 is put in direct contact with the solid object 18 which in turn is in effective contact with the cell 14 through the light source 26 and the polarizer 22. The latter two objects of course will have to transmit ultrasonic waves well. Such flat light sources might be created by electroluminescence, phosphorescence, or perhaps even difusing plate sidelights. Again any one or more of the individual elements of the inventive device may be incorporated as a part of one or more of the other items so long as the necessary function is achieved.

The device of FIG. 4 is similar to FIG. 3 except that only one polarizer 28 is used and the light source 26 is on the same side as the cell 14 as the viewer 17, physically separated from the coupling between the sound generator 16, the object 18, and the cell 14. In this arrangement, the light from the source 26 is polarized as it passes through polarizer 28, falls upon the reflecting mirror 42 positioned beyond the liquid crystal layer 34, and is reflected back through polarizer 28 (after having been acted upon by the birefringence of the layer 34) to give the desired image to the viewer 17.

As can be noted in FIG. 1, and particularly in FIG. 5, the ultrasonic radiation of the piezo-optic cell can be at an angle as well as perpendicular to the surface. In the present experimental system, acoustical energy of about 0.5 watts per square inch is needed to create images on the piezo-optic cells made with lecithin and nematic liquid crystal MBBA in accordance with the aforementioned patent disclosure. Of course, considerably less energy can be used with efficient systems according to the present invention.

The object 18 schematically indicated in FIG. 5 is a bone specimen. The sonic waves from the sonic generator 16 are reflected off the back of cell 14 onto the specimen l8 and back onto the cell 14. By careful adjustment of the frequency to tune it to the structural dimensions of the scull bone, a patterned image was viewed on the cell 14 depicting the internal structure of the scull bone.

In FIG. 6, a sonic generator 16 with a right angle prism shaped head acting as the object 18 has engraved in one flat side thereof a hole 20 in the shape of a flat E. The object 18 was placed in direct contact with the edge of the piezo-optic cell 14 and the viewer located at 17 could see the floating" image of the engraved E in the cell 14.

Note that the object to be viewed need not be a solid, but can be liquids with different densities or even can be a virtual object such as music.

I claim:

1. A mechanical wave-optical converter imaging device for visualizing a mechanical wave pattern image, for example of an object, comprising a piezo-optic visual display cell, having a thin layer of aligned liquid crystals, means for polarized transillumination of said cell, a mechanical wave image generating source oriented to be incident on said cell, and analyzing means for observing the changes in birefringence occasioned by the action of the mechanical waves in a patterned image on the liquid crystal layer of the piezo-optic cell.

2. A device as claimed in claim 1, wherein the mechanical waves are acoustic waves and said liquid crystal layer has a thicknessless than 0.010 inches.

3. A device as claimed in claim 1 further comprising coupling means for effectively coupling said cell, object and source efficiently to transmit said mechanical waves therebetween, wherein said mechanical waves are acoustic waves, said source is an acoustic transducer oriented to impinge upon said object so as to cause a wave-form image thereof to be incident on said cell, and said liquid crystal layer has a thickness small enough to view said image.

4. A device as claimed in claim 3, wherein the mechanical wave generating source is an acoustic transducer positioned to trans-sonify the object to be incident on said cell.

5. A device as claimed in claim 4 wherein the mechanical wave generating source further comprises a sonic focusing means between said transducer and said cell.

6. A device as claimed in claim 5 wherein said liquid crystals are nematic.

7. A device as claimed in claim 2, wherein the mechanical wave generating source is an acoustic transducer positioned to insonify said cell with acoustic waves reflected from said object.

8. A device as claimed in claim 2, wherein the mechanical wave generating source is an acoustic transducer positioned to form a solid coupling to a face of said cell.

9. A device as claimed in claim 8 comprising a light source positioned to be incident on the viewing side of said cell through the polarized analyzing means, and a mirror on the opposing cell face which is in contact with said coupling means whereby the light source, analyzer and mirror combine to form said polarizing means.

10. A device as claimed in claim 3, wherein the mechanical wave generating source is an acoustic transducer positioned to form a solid coupling to an edge of said cell.

1 1. A device as claimed in claim 3 for creating visualized acoustic holograms comprising a means for generating and directing reference acoustic waves on said cell in coherence and overlap with said object acoustic waves.

12. A device as claimed in claim 3, wherein said cell has a multiplicity of liquid crystal layers each having a thin transparent spacer.

13. A device as claimed in claim 3 wherein the thickness of said liquid crystal layer is governed by the following equation FH /C less than or equal to K, wherein H is the thickness of the liquid crystal layer, C is the velocity of the acoustic wave in the crystal layer, F is the frequency and K is a constant for the given device.

14. A device as claimed in claim 2 wherein said liquid crystals are nematic.

15. A method of forming a real-time visual image of an acoustic wave pattern image of objects, comprising the steps of treating at least one interface surface formed of a layer of liquid crystals and of its surrounding environment with a lubricant to reduce the surface orientation of the environment on said liquid crystals, insonifying the objects to be viewed and directing the acoustic wave pattern image thus formed focused onto a layer of liquid crystals the thickness of which is small enough to assure clarity of the resulting visual image, transilluminating the layer with polarized light and viewing the thus illuminated layer with an analyzer.

16. A method as claimed in claim 15 for creating visualized acoustic holograms comprising generating and directing reference acoustic waves on said cell in coherence and overlap with said object acoustic waves.

17. A method according to claim 15 comprising using said method for acoustic radar by reflective insonification of said objects.

18. A method as claimed in claim 15 wherein said liquid crystals are nematic.

19. A method according to claim 18 wherein said lubricant is lecithin and said liquid crystal layer is less than 0.010 inches thick.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent: No. 3,83ll434 Dated Angngt 27. 1914 Inventor(s) Pal Greguss It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 1, column 9, line 10, delete "aligned"; and

Claim 1, column .9, line 11, after "crystals" insert --functioning as though substantially in the free state-.

Signed and sealed this 14th day of January 1975.

(SEAL) Attest: I

McCOY M. GIBSON JR. c. MARSHALL DANN Arresting Officer Commissioner of Patents I ORM PO-OSO (069) USCOMM-DC 6O376-P69 U.S, GOVERNMENT PRINTING OFFICE I969 0-366-334 UNITED STATES PATENT OFFICE- CERTIFICATE OF CORRECTION Patent No. 3 I 1: 434 I Date-d August 27 1974 lnventor(s) Pal reguss It is. certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as. shown below:

Claim 7, "2 should be -3-; Claim 8, she- 11d b --3--;

Claim 14 '2 should be 3-.

Signed and sealed this 3rd day of December 1974.

(SEAL) Attest: v I

McCOY M'. GIBSON JR. c. MARSHALL DANN I a Attesting Officer Commissioner of Patents FORM Po-w o (10-69) r USCOMM-DC 0376-l 69 I v & U.5. GOVERNMENT PRINTiNG OFFICE 2 I959 0-366-33, 

1. A mechanical wave-optical converter imaging device for visualizing a mechanical wave pattern image, for example of an object, comprising a piezo-optic visual display cell, having a thin layer of aligned liquid crystals, means for polarized transillumination of said cell, a mechanical wave image generating source oriented to be incident on said cell, and analyzing means for observing the changes in birefringence occasioned by the action of the mechanical waves in a patterned image on the liquid crystal layer of the piezo-optic cell.
 2. A device as claimed in claim 1, wherein the mechanical waves are acoustic waves and said liquid crystal layer has a thickness less than 0.010 inches.
 3. A device as claimed in claim 1 further comprising coupling means for effectively coupling said cell, object and source efficiently to transmit said mechanical waves therebetween, wherein said mechanical waves are acoustic waves, said source is an acoustic transducer oriented to impinge upon said object so as to cause a wave-form image thereof to be incident on said cell, and said liquid crystal layer has a thickness small enough to view said image.
 4. A device as claimed in claim 3, wherein the mechanical wave generating source is an acoustic transducer positioned to trans-sonify the object to be incident on said cell.
 5. A device as claimed in claim 4 wherein the mechanical wave generating source further comprises a sonic focusing means between said transducer and said cell.
 6. A device as claimed in claim 5 wherein said liquid crystals are nematic.
 7. A device as claimed in claim 2, wherein the mechanical wave generating source is an acoustic transducer positioned to insonify said cell with acoustic waves reflected from said object.
 8. A device as claimed in claim 2, wherein the mechanical wave generating source is an acoustic transducer positioned to form a solid coupling to a face of said cell.
 9. A device as claimed in claim 8 comprising a light source positioned to be incident on the viewing side of said cell through the polarized analyzing means, and a mirror on the opposing cell face which is in contact with said coupling means whereby the light source, analyzer and mirror combine to form said polarizing means.
 10. A device as claimed in claim 3, wherein the mechanical wave generating source is an acoustic transducer positioned to form a solid coupling to an edge of said celL.
 11. A device as claimed in claim 3 for creating visualized acoustic holograms comprising a means for generating and directing reference acoustic waves on said cell in coherence and overlap with said object acoustic waves.
 12. A device as claimed in claim 3, wherein said cell has a multiplicity of liquid crystal layers each having a thin transparent spacer.
 13. A device as claimed in claim 3 wherein the thickness of said liquid crystal layer is governed by the following equation FH1/C less than or equal to K, wherein H1 is the thickness of the liquid crystal layer, C is the velocity of the acoustic wave in the crystal layer, F is the frequency and K is a constant for the given device.
 14. A device as claimed in claim 2 wherein said liquid crystals are nematic.
 15. A method of forming a real-time visual image of an acoustic wave pattern image of objects, comprising the steps of treating at least one interface surface formed of a layer of liquid crystals and of its surrounding environment with a lubricant to reduce the surface orientation of the environment on said liquid crystals, insonifying the objects to be viewed and directing the acoustic wave pattern image thus formed focused onto a layer of liquid crystals the thickness of which is small enough to assure clarity of the resulting visual image, transilluminating the layer with polarized light and viewing the thus illuminated layer with an analyzer.
 16. A method as claimed in claim 15 for creating visualized acoustic holograms comprising generating and directing reference acoustic waves on said cell in coherence and overlap with said object acoustic waves.
 17. A method according to claim 15 comprising using said method for acoustic radar by reflective insonification of said objects.
 18. A method as claimed in claim 15 wherein said liquid crystals are nematic.
 19. A method according to claim 18 wherein said lubricant is lecithin and said liquid crystal layer is less than 0.010 inches thick. 